The permanent alteration of the color of keratinous fibers, in particular human hair, by the application of hair dyes is well known. Oxidative hair dye precursors, i.e., developers (also called primary intermediates) and couplers diffuse into the hair through the cuticle and into the cortex. The precursors combine in the presence of an oxidizing agent, such as hydrogen peroxide, to form larger-sized dye molecules that result in a visual color of the hair (“end hair color”). Different combinations of developers and couplers produce different shades of hair color when combined with the oxidizing agent. The end hair color is not easily predicted given the complex chemical process that occurs to achieve an end hair color.
Permanent hair colorant formulations should produce end hair colors that are stable for at least 4 to 6 weeks. Additionally, the end hair color should exhibit good washfastness, good lightfastness, fastness to rubbing, as well as sufficient resistance with respect to perspiration. Preferably, it should be possible to produce a broad palette of different color shades by combining suitable developers and couplers.
Hair colorant formulations generally provide acceptable and immediate results. However, achieving both desired shade (hue) and depth of shade (chroma) remains challenging, particularly for hair colorant formulations that impart a blue with less violet overtones to the hair. To achieve desirable shades in the blue area, a combination of 1-4-diaminobenzene compounds with 2,6-diaminopyridine may be used. Nevertheless, the shades may fail to provide the desirable hue and chroma and, thereby, the hair colorant formulation may fall short of producing the desired end hair color.
U.S. Pat. No. 3,200,040 discusses the dyeing of hair with coupler and primary compounds based on diaminopyridines. The combination of p-toluenediamine with 2,6-diaminopyridine in an aqueous ammonia solution and mixed with 6% hydrogen peroxide gives a strong blue color. There are other developers used that give different shades of blue, but they may not be available to use from a toxicological standpoint and may give very different performance with other couplers compared to 1,4-diaminobenzene based developers, which increases the complexity of development for marketable hair color formulations.
There remains an ongoing need for additional hair colorant compositions that can provide desirable blue shades with less violet overtones, particularly when used with various oxidant systems, i.e., ammonium carbonate, hydrogen peroxide, and, optionally, a radical scavenger and/or chelant.